BOSTON — When it comes to discussing Rajon Rondo, Kris Humphries has a luxury of freedom not every member of the Celtics has.

Unlike some of his teammates, Humphries has been in Boston for less than a year, with the possibility of bolting via free agency this summer. He’s had a couple of public run-ins with Rondo in the past. As a result, he doesn’t need to pretend he and the All-Star point guard are best friends, lest he see fewer of those pinpoint passes head his way.

So whereas the company line from Celtics big men always has been that Rondo makes their jobs simple, to just catch and convert the easy shot, Humphries is comfortable giving a more honest assessment.

“He’s a tricky guy, because sometimes, as a big, you don’t know when he’s going to throw you the ball,” Humphries said. “He’s breaking down the D and making passes that you may not even see coming, so it’s taken a while to get used to being ready when he breaks down a defense.”

Rondo was at his best Sunday, handing out 18 assists without committing a turnover while leading the Celtics to a victory over the Detroit Pistons. He became the 11th player since 1985 to record that many assists without a turnover, and Humphries was a major beneficiary, as was Jeff Green. Humphries scored 20 points, while Green erupted for a team-high 27 points, with Rondo’s passing game rubbing off on his teammates. The Celtics totaled 38 assists on 47 field goals while committing just seven turnovers.

All of this occurred with Rondo not yet at full strength. Sunday’s game was just his 18th since his return from a torn ACL. As brilliant as he was against the Pistons, he struggled two games earlier against the Golden State Warriors and Stephen Curry, who has passed Rondo on the list of the NBA’s best point guards in most experts’ minds.

Rondo will get another shot at Curry in the future, perhaps when he doesn’t wake up the morning after games with soreness in his knee, Achilles and calves. It’s the Achilles that bothers him the most, which is why he has yet to suit up for consecutive games in back-to-back sets. That remains the case this week, as Rondo is not expected to play in Wednesday’s home game against the New York Knicks.

Celtics coach Brad Stevens therefore isn’t ready to say Rondo is officially “back” — not even after performances like Sunday’s.

“It’s hard for me to say that he’s where he ultimately can be, because every game he gets a little better,” Stevens said. “Hopefully, he just continues to feel better and get better.”

Stevens isn’t being unreasonably demanding, either. Rondo agrees with him. Asked if he is fully recovered, Rondo offered a firm “no.” He’s not yet the player who made four All-Star teams and twice led the NBA in assists, he says. But he’s getting there.

“It’s an NBA season — it’s tough,” Rondo said. “I’m up to 34, 35 minutes a night now. I’m doing the right procedures, I’m taking a massage, I’m icing after the games. I’m doing what I’m supposed to do. It’s just that I have to listen to my body.”